The present invention relates generally to computer-aided design (CAD), manufacturing (CAM) and engineering (CAE), and product data management (PDM II) systems and to a system and method for controlling the shape of reflection lines on the surface of an object in such CAD, CAM, CAE or PDM II systems. More particularly, the present invention provides for direct control of the reflection line and the modification of the shape of an object to correspond to a desired reflection line on the surface of the object.
CAD systems are widely used for many types of design and manufacturing applications. Certain of these applications can be very costly in terms of user interaction time. One such interaction intensive application is object or surface design and modification.
In the computer-aided design and manufacturing of many end products, particularly those which are intended for the consumer market, the external appearance of the product plays a major role. The car industry provides a good example of this well-known fact. One significant aspect of the external appearance of the product is the way in which its surface reflects the light in the room where the product is presented to prospective buyers. This can be a car dealer showroom where neon tubes provide most of the light in the room and the prospective buyers see the reflection of the neon light as reflection lines on the external surface of the cars. It has been shown that smooth reflection lines tend to leave the consumer with a better impression of the product than erratic or misshapen reflection lines. This is why the design stylists in many consumer product manufacturing companies spend a lot of time trying to ensure that the end product will exhibit smooth reflection lines when presented in a showroom. They need to do that at the design stage, of course, before the product goes into production. It is therefore important for a CAD/CAM/CAE/PDM II application to offer design stylists the opportunity to control to the greatest extent possible the way the surface of the designed product will reflect light.
In the currently available systems, the surface of the object being designed is displayed to the user with a simulation of the reflection of a light source, say an elongated neon light source, system allows the user to alter the shape of the surface by means of free-form surface shape design techniques. Then the new reflection line is shown to the user and the process is repeated until the user is reasonably satisfied with what appears on the computer. In this process the user has no direct control over the reflection line: for the software functionalities the reflection line is only a xe2x80x9cby-productxe2x80x9d of the shape of the surface, whereas in many cases it is the ultimate goal of the user. This is a long and tedious trial-and-error process. There is a need for a system which would allow the user to define up front the reflection line the surface should preferably exhibit and which would then reshape the surface to attain or approximate this kind of reflection line.
A method for surface design and modification is described in an article titled Energy-Based Models for Free-Form Surface Shape Design, by George Celniker and David Gossard, ASME Design Automation Conference, February 1989, and in an article titled Linear Constraints for Deformable B-Spline Surfaces, by George Celniker and Will Welch, Association for Computing Machinery, 165-70, 1992 (Celniker et al.). In these articles a system is described which provides for the modification of the shape of a deformable surface. The system applies constraints defined by the user to the entire surface while attempting to reach an equilibrium. All changes to a surface reflect a minimization of a global energy function of the surface. Additionally, all curves are constrained by requiring an equilibrium which fixes each point and the shape of the entire curve. When using such a system for arriving at a desired (subjective) degree of smoothness for a surface, a user will often have to modify several times one or more constraints, which causes the system to go through several iterations in each of which the surface must be recalculated and displayed to the user, until the user finds the result acceptable. Celniker""s constraint based model attempts to generate a smooth shape within the constraints imposed by the user, but does not address the issue of direct control of reflection lines or indirect control of the surface of an object through the use of its reflection lines.
Two different methods for surface modification are described in an article titled Correction of Local Surface Irregularities Using Reflection Lines, by Reinhold Klass, Computer Aided Design, Vol. 12, No. 2, March 1980, pp. 73-77, and in an article titled Smoothing Surfaces Using Reflection Lines for Families of Splines, by E. Kaufmann and R. Klass, Computer Aided Design, Vol. 20, No. 6, July/August 1988, pp. 312-16. These articles both describe methods for modifying a surface using reflection lines. Neither method provides for any surface constraints besides for the reflection line. These methods differ from Celniker et al. in that neither is based on a constraint based energy minimization model to guarantee global control of the surface, and no provision exists for introducing such a model. The lack of constraints other than the reflection line means that it is not possible to guarantee that the surface will not move at its boundaries. These methods demand large amounts of processing, and memory by requiring numerous calculations and reiterations to arrive at the desired reflection lines. Additionally, several user interaction may be necessary to insure that the surface shape provides the desired characteristics.
A further method for surface modification is described in an article titled Direct Highlight Line Modification on NURBS Surfaces, by Chen et al., Computer Aided Geometric Design 14 (1997) 583-601. This article describes a method for modifying a surface using highlight lines. The highlight lines differ from reflection lines in that they are viewer independent, i.e., not based on any viewer perspective, and are not subject to change based on a viewer""s perspective. Thus, highlight lines are simpler to implement than reflection lines, but do not provide a realistic model for surface design or modification.
The various methods described in the literature for object modification using CAD systems are limited since they do not provide for object modification based on reflection line control while providing for constraints on the object being modified, and in consequence require time consuming user interaction to arrive at the desired result.
The present invention solves these problems and provides an apparatus and method for modifying the shape of an object, for example, a surface, by using reflection lines, while at the same time maintaining certain constraints on the object being modified. By using reflection lines an object may be modified based on a realistic viewer perspective.
The present invention provides an apparatus and method for modifying the shape of an object, for example, a surface, by defining the shape and/or position of one or more lines along which a light source is reflected by the object (reflection line). Based upon a change, such as, for example, the position and/or shape, to one or more of the reflection lines, the system modifies the shape of the object to correspond to the new surface requirements as defined by one or more of the modified reflection lines, while maintaining the constraint on the object as predetermined by the system or user. The light source may be any type of light source, such as, for example, a linear neon or fluorescent light, or a curved neon or fluorescent light.
The apparatus according to the present invention utilizes a CAD system, and provides for control of the reflection line using a control device, for example, a cursor control device, such as a mouse, a roller ball, a pressure pad, or a capacitance or inductance based pad, or for example, an interactive display device, such as a light pen, or a touch screen. The apparatus includes a processor programmed to determine the shape of the object, for example, a surface or a set of adjacent surfaces, based on either one or more selected reflection lines. The processor can be programmed to use energy minimization algorithms to make these determinations. The processor may also be programmed to determine one or more reflection lines approximating one or more desired reflection lines, which are merely targets for the actual reflection lines, based on an attraction to one or more of the desired reflection lines. This may be implemented using vector-to-vector springs.
By defining one or more reflection lines, a user is effectively and indirectly controlling the shaping of an object by the system. This is useful for all types of object design activities, including, for example, surface design used in aircraft (for example, for critical air flow requirements), auto body design (for example, for aesthetic requirements) and bottle design (for example, perfume bottles). The reflection line is set by the user or reset from a current setting to a defined setting and the system shapes (in the case of a flat or initial surface) or modifies the shape of the surface to correspond to the defined setting, with the defined setting becoming the new setting of the reflection line and the system determined shape or system modified shape becoming the new shape of the surface.
The reflection line and corresponding surface may be modified absolutely, i.e., by imposing on the surface that it include a user input curve as a reflection line, or they may be modified by attraction, i.e., by considering the user input curve to be a target to which the reflection line on the surface is pulled by a force or loading. Each approach has certain advantages and disadvantages. Absolute modification instantly guarantees that the surface will exhibit the desired reflection line. However, by imposing such a strong constraint on this line, the surface can generate undesirable characteristics in other areas, because the system may become overconstrained. Modification by attraction in most cases yields better surface behavior because the reflection line is allowed to deviate slightly from the target in order to avoid an overconstrained condition.
Modification of a surface may be accomplished by user control of the reflection line. The system adjusts the surface to correspond to the new reflection line as defined by the user. The system determines the normal vectors to an imaginary surface, based on a predetermined linear light source and observer, which would correspond to the defined reflection line. The system then adjusts the surface to correspond to the determined normal vectors representing the imaginary surface. Although it is possible for a number of surface shapes to correspond to the defined reflection line, the preferred strategy is to select a shape based on energy minimization. In the scenario of modification by attraction, the adjustment of the surface to correspond to the determined normal vectors may be accomplished by a vector to vector spring load.
A method utilizing energy minimization determines a new shape for the surface based on the lowest change in energy from the shape being modified, such as, for example, an initial flat plane or a previous design. This energy may be defined, for example, as a sum of the integral of stretch and of bending of the surface.
Although there may be a displacement of each point on a surface from a position in space as defined by the original surface to a different position in space as defined by the new surface due to the modification of the surface by the system, such displacements are sufficiently small to allow satisfactory results despite not been taken into account as part of the system""s determination.
The system, apparatus and method according to the present invention may be implemented, for example, as computer readable program code and may be contained in or on, or placed into or onto a computer usable medium, such as, for example, a CD ROM, hard drive, computer disc, computer tape, optical storage medium, magnetic storage medium, electronic storage medium, chemical storage medium, EEPROM, RAM, or any other medium now known or which may become known in the future. The system, apparatus and method according to the present invention may also be implemented as a computer program product, such as, for example, a computer file or files, for use with a graphic display or some other display device, such as, for example, a printer or plotter, holographic display, or virtual reality display device, having computer readable program code which can be stored in or on an electrical, magnetic, chemical, optical, mechanical or audio storage medium or any other storage medium now know or which hereinafter becomes known.
The system, apparatus and method according to the present invention may also be transferred via hard copy, electronic transfer, such as, for example, via the internet, intranet, WAN, LAN, email, or via any other medium, such as, for example, any of the media previously described herein, or as a computer data signal embodied in a data stream, such as, for example, a digital, analog or optical data stream.
A more detailed description of preferred embodiments of the present invention is set forth below.